A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes "open" and "close" electromagnets which, when energized, produce an electromagnetic force on an armature. The armature is biased by a pair of springs arranged in parallel. The armature is coupled with a gas exchange valve of the engine. The armature rests approximately half way between the open and close electromagnets when the springs are in equilibrium. When the armature is held by a magnetic force in either the closed or opened position (at rest against the open or close electromagnet), potential energy is stored by the springs. If the magnetic force is shut off with the armature in the opened position, the spring's potential energy will be converted to kinetic energy of the moving mass and cause the armature to move towards the close electromagnet. If friction is sufficiently low, the armature can then be caught in the closed position by applying current to the close electromagnet.
When an actuator is installed in a vehicle the armature has to be centered between the two electromagnets. This is typically done by adjusting the compression of the upper spring of the actuator. Once the center position is found, the spring must remain in the compressed state associated with the centered armature. The slightest change in the compression of the upper spring will result in an un-centered armature, which may cause improper operation of the actuator.
Thus, there is a need to provide a spring assembly for an electromagnetic actuator which permits fine adjustment to center the armature between two electromagnets, and once centered, prevents further adjustment of the compression of the spring and thus, the position of the armature.